(1) Field of the Invention
The invention relates to a purge plug, containing a refractory material, configured to be inserted in the bottom of a ladle for introducing purging gas through a heat of molten metal in the ladle.
(2) Description of the Related Art
The steel manufacturing process makes use of a vessel, called a ladle, which is lined with a refractory material to contain the molten steel. A purge plug is a device, installed in a passage through the exterior of the ladle, which is configured to introduce gas into the interior of the ladle. The plug may incorporate pores or passages to permit gas flow. The function of the purge plug is to provide gas stirring of the molten metal, thereby promoting thermal and chemical homogenization. The purging gas may also modify the heat (molten contents of the ladle). Stirring is normally accomplished by percolating argon or nitrogen gas through the purge plug in the bottom of the ladle. Typically, a purge plug has the shape of a truncated ceramic cone (frustum) and is enclosed in a sheet-metal casing.
In a typical configuration, the purge plug is replaceably mounted in a housing block installed in the bottom of the ladle. In the ladle, various high-temperature processes are carried out in which the purge plug is crucial. The purge plug is worn heavily during the process in its uppermost portion, which is directed towards the heat, and regularly has to be replaced by a new purge plug when its height has shrunk to a minimum permissible level. In addition, the portion of the housing block surrounding the uppermost portion of the purge plug experiences erosion. Consequently, the lateral surfaces of the purge plug are increasingly exposed to erosion as the housing block erodes, and the area of the housing block in contact with the purge plug decreases. Results of decreased contact area include mechanical instability, failure of refractory components and increased probability of breakout.
In many steel shops it is common practice to bomb or gun around a new plug installed in a used or worn housing block in order to fill any void in a worn block and to build up the ladle bottom around the newly installed plug. This procedure adds to the life of the plug installed in the worn housing block. Bombing around the new plug involves dropping refractory material from the top of the ladle around the newly installed plug in a worn housing block. Gunning involves shooting refractory material with a gunning machine against the ladle bottom and housing block surrounding the new plug in a worn housing block.
Gunning or bombing around the plug does increase the life of the plug and housing block. However in many cases the material will shear off the top of the housing block exposing the steel can of the purge plug to liquid steel. This liquid metal contact melts the steel can and the purge plug will usually shear off to a level at a height where solid refractory material surrounds the purge plug.
Plug life is greatly affected by how well the material deposited by ladle bomb or by gunning stays in place around the purge plug. The application of cement around the purge plug may leave gaps and voids that are subject to infiltration and increased erosion rate of the repaired piece. Replacement purge plugs currently in use are configured with a smooth radial surface that facilitates the placement of the purge plug in the housing block, but does not facilitate the bonding of the radial surface of the purge plug to the material deposited by ladle bombing or gunning.
If the repair, by ladle bomb or gunning, around the purge plug can be made to stay in place, plug shearing will be reduced and both plug life and housing block life will be increased. There still exists a need for a process or configuration for repair of the housing block in which the purge plug is anchored to the housing block to prevent infiltration, and the housing block is anchored to the purge plug to prevent portions of the repaired housing block from working free. There also exists a need for a process or configuration for repair of refractory pieces with similar configurations, such as well blocks around the inner nozzle of a slide gate.